In recent years, SiC (silicon carbide) semiconductors which permit an operation with higher breakdown voltage, higher current and lower ON resistance than Si semiconductors are attractive as power device materials alternative to Si semiconductors (see, for example, Patent Literature 1).
SiC power devices are used, for example, as switching devices for various invertor circuits to be incorporated in motor control systems, power conversion systems and the like.
In a motor control circuit or the like, such a SiC power device (switching device) is designed so that, when current flowing through a motor coil is cut off by turning off the SiC power device, a counter electromotive voltage generated in the motor coil due to electromagnetic induction of the motor coil is consumed by a diode.
More specifically, current attributable to the counter electromotive voltage is allowed to flow into the motor coil as return current by the rectification function of a parasitic diode (body diode) defined by a pn junction between a p-type body region and an n-type drift region present in the device. This prevents a high counter electromotive voltage from being applied to the switching device.